1. Field of the Invention
The present invention relates to a method of producing a monoalkylether of a dihydric phenol compound. More particularly, the present invention relates to a method of producing a monoalkylether of a dihydric phenol compound at a high conversion and selectivity by a catalytical dehydration reaction of a dihydric phenol compound with a lower monohydric alcohol in the presence of a specific dehydration reaction catalyst comprising aluminum, phosphorus, titanium, silicon, a member selected from alkali metals (Group Ia) alkaline earth metals (Group IIa) and metals of Group VIII of the Periodic table, and oxygen in a specific atomic ratio.
The specific dehydration reaction catalyst exhibits an excellent durability in a continuous dehydration reaction of the dihydric phenol compound with the lower monohydric alcohol in a gas phase over a long time, and a high mechanical strength.
The monoalkylethers of dihydric phenol compounds, for example, guaiacol and guathol, are useful as intermediate of various perfumes and medicines, or as antioxidants and stabilizers of synthetic resins.
2. Description of the Related Arts
It is known that a monoalkylether of a dihydric phenol compounds, for example, guaiacol or guathol, can be produced by a catalytic dehydration (etherification) reaction of a dihydric phenol compound with a lower monohydric alcohol in a gas phase.
In a conventional method, a monoalkylether of a dihydric phenol compound, is produced by etherifying in a liquid phase a dihydric phenol compound with an alkylating agent consisting of, for example, dimethyl sulfate, a combination of alkyl chloride with an alkali, or dimethyl carbonate. Generally, the alkylating agent usable for the liquid phase etherifying process is extremely expensive, and thus the waste liquid from the etherifying process must be clarified by a complicated process.
Various gas phase etherifying processes for producing the monoalkylethers of the dihydric phenol compounds are disclosed in the following literature:
(1) Chem. Abs., 55-7366 (1960), Masloboino-Zhirovaya Prom., 26[10], 24 to 27 (1960) PA0 (2) West German Patent No. 827803 PA0 (3) Japanese Examined Patent Publication No. 53-35062 PA0 (4) Japanese Examined Patent Publication No. 55-33658 PA0 (5) Japanese Examined Patent Publication No. 55-6618 PA0 (6) Journal of Japan Chemical Association, [12], 23311 (1985), and Japanese Examined Patent Publication No. 56-25213
For example, an etherifying reaction of a dihydric phenol compound, for example, catechol, with a lower monohydric alcohol, for example, methyl alcohol, is carried out in a gas phase in the presence of (a) a catalyst prepared from phosphoric acid and boric acid, as disclosed in literatures (1) and (2), (b) another catalyst comprising aluminum, phosphorus, boron and oxygen, as disclosed in literatures (3), (4) and (5), or (c) still another catalyst consisting of kaolin, as disclosed in literatures (6), to produce a monoalkylether of the dihydric phenol compound, for example guaiacol.
The prior art disclosed in literatures (1) and (2), in which the catalyst (a) comprises phosphoric acid and boric acid, is disadvantageous in that the conversion to the monoalkylether is made at an unsatisfactory level of 80 to 90%, and an active catalytic component produced by the reaction of phosphoric acid with boric acid, i.e., boron phosphate (BPO.sub.4), is consumed with a lapse of time, and therefore, the durability of the catalyst is not long enough for industrial use.
The prior art process disclosed in literatures (3), (4) and (5) in which the catalyst (b) comprises aluminum, boron, phosphorus, and oxygen is advantageous in that the conversion to the monoalkylether of the dihydric phenol compound is high and the duration of the BPO.sub.4 is improved, but is disadvantageous in that the activity of the catalyst is reduced with a lapse of time during a long time operation, due to the consumption of BPO.sub.4 and an adhesion of carbon to the catalyst surface, and the mechanical strength is also gradually lowered with a lapse of time. Therefore, the durability of the catalyst must be further improved. Further, this catalyst is disadvantageous is that, when a lowering of the activity of the catalyst occurs, the reaction temperature must be raised in line with this lowering of the catalyst activity, to maintain the conversion of the dihydric phenolic compound to the monoalkylether thereof at a desired high level, and therefore, it is very difficult to continue the etherifying reaction in a stable condition for a long time.
In the process in which the catalyst (c) consisting of kaolin is used, the conversion to the alkylether of the dihydric phenol compound is obtained at an unsatisfactory low level of about 80%, and an undesirable by-product is formed in a large amount of about 10%. Therefore, this process is not practical for industrial use.